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#' Do columns in the table (and their types) match a predefined schema?
#'
#' @description
#'
#' The `col_schema_match()` validation function, the `expect_col_schema_match()`
#' expectation function, and the `test_col_schema_match()` test function all
#' work in conjunction with a `col_schema` object (generated through the
#' [col_schema()] function) to determine whether the expected schema matches
#' that of the target table. The validation function can be used directly on a
#' data table or with an *agent* object (technically, a `ptblank_agent` object)
#' whereas the expectation and test functions can only be used with a data
#' table.
#'
#' The validation step or expectation operates over a single test unit, which is
#' whether the schema matches that of the table (within the constraints enforced
#' by the `complete`, `in_order`, and `is_exact` options). If the target table
#' is a `tbl_dbi` or a `tbl_spark` object, we can choose to validate the column
#' schema that is based on R column types (e.g., `"numeric"`, `"character"`,
#' etc.), SQL column types (e.g., `"double"`, `"varchar"`, etc.), or Spark SQL
#' types (e.g,. `"DoubleType"`, `"StringType"`, etc.). That option is defined in
#' the [col_schema()] function (it is the `.db_col_types` argument).
#'
#' There are options to make schema checking less stringent (by default, this
#' validation operates with highest level of strictness). With the `complete`
#' option set to `FALSE`, we can supply a `col_schema` object with a partial
#' inclusion of columns. Using `in_order` set to `FALSE` means that there is no
#' requirement for the columns defined in the `schema` object to be in the same
#' order as in the target table. Finally, the `is_exact` option set to `FALSE`
#' means that all column classes/types don't have to be provided for a
#' particular column. It can even be `NULL`, skipping the check of the column
#' type.
#'
#' @inheritParams col_vals_gt
#'
#' @param schema *The table schema*
#'
#'   `obj:<col_schema>` // **required**
#'
#'   A table schema of type `col_schema` which can be generated using the
#'   [col_schema()] function.
#'
#' @param complete *Requirement for columns specified to exist*
#'
#'   `scalar<logical>` // *default:* `TRUE`
#'
#'   A requirement to account for all table columns in the provided `schema`. By
#'   default, this is `TRUE` and so that all column names in the target table
#'   must be present in the schema object. This restriction can be relaxed by
#'   using `FALSE`, where we can provide a subset of table columns in the
#'   schema.
#'
#' @param in_order *Requirement for columns in a specific order*
#'
#'   `scalar<logical>` // *default:* `TRUE`
#'
#'   A stringent requirement for enforcing the order of columns in the provided
#'   `schema`. By default, this is `TRUE` and the order of columns in both the
#'   schema and the target table must match. By setting to `FALSE`, this strict
#'   order requirement is removed.
#'
#' @param is_exact *Requirement for column types to be exactly specified*
#'
#'   `scalar<logical>` // *default:* `TRUE`
#'
#'   Determines whether the check for column types should be exact or even
#'   performed at all. For example, columns in R data frames may have multiple
#'   classes (e.g., a date-time column can have both the `"POSIXct"` and the
#'   `"POSIXt"` classes). If using `is_exact == FALSE`, the column type in the
#'   user-defined schema for a date-time value can be set as either `"POSIXct"`
#'   *or* `"POSIXt"` and pass validation (with this column, at least). This can
#'   be taken a step further and using `NULL` for a column type in the
#'   user-defined schema will skip the validation check of a column type. By
#'   default, `is_exact` is set to `TRUE`.
#'
#' @return For the validation function, the return value is either a
#'   `ptblank_agent` object or a table object (depending on whether an agent
#'   object or a table was passed to `x`). The expectation function invisibly
#'   returns its input but, in the context of testing data, the function is
#'   called primarily for its potential side-effects (e.g., signaling failure).
#'   The test function returns a logical value.
#'
#' @section Supported Input Tables:
#'
#' The types of data tables that are officially supported are:
#'
#'  - data frames (`data.frame`) and tibbles (`tbl_df`)
#'  - Spark DataFrames (`tbl_spark`)
#'  - the following database tables (`tbl_dbi`):
#'    - *PostgreSQL* tables (using the `RPostgres::Postgres()` as driver)
#'    - *MySQL* tables (with `RMySQL::MySQL()`)
#'    - *Microsoft SQL Server* tables (via **odbc**)
#'    - *BigQuery* tables (using `bigrquery::bigquery()`)
#'    - *DuckDB* tables (through `duckdb::duckdb()`)
#'    - *SQLite* (with `RSQLite::SQLite()`)
#'
#' Other database tables may work to varying degrees but they haven't been
#' formally tested (so be mindful of this when using unsupported backends with
#' **pointblank**).
#'
#' @section Actions:
#'
#' Often, we will want to specify `actions` for the validation. This argument,
#' present in every validation function, takes a specially-crafted list object
#' that is best produced by the [action_levels()] function. Read that function's
#' documentation for the lowdown on how to create reactions to above-threshold
#' failure levels in validation. The basic gist is that you'll want at least a
#' single threshold level (specified as either the fraction of test units
#' failed, or, an absolute value), often using the `warn_at` argument. Using
#' `action_levels(warn_at = 1)` or `action_levels(stop_at = 1)` are good choices
#' depending on the situation (the first produces a warning, the other
#' `stop()`s).
#'
#' @section Labels:
#'
#' `label` may be a single string or a character vector that matches the number
#' of expanded steps. `label` also supports `{glue}` syntax and exposes the
#' following dynamic variables contextualized to the current step:
#'
#' - `"{.step}"`: The validation step name
#'
#' The glue context also supports ordinary expressions for further flexibility
#' (e.g., `"{toupper(.step)}"`) as long as they return a length-1 string.
#'
#' @section Briefs:
#'
#' Want to describe this validation step in some detail? Keep in mind that this
#' is only useful if `x` is an *agent*. If that's the case, `brief` the agent
#' with some text that fits. Don't worry if you don't want to do it. The
#' *autobrief* protocol is kicked in when `brief = NULL` and a simple brief will
#' then be automatically generated.
#'
#' @section YAML:
#'
#' A **pointblank** agent can be written to YAML with [yaml_write()] and the
#' resulting YAML can be used to regenerate an agent (with [yaml_read_agent()])
#' or interrogate the target table (via [yaml_agent_interrogate()]). When
#' `col_schema_match()` is represented in YAML (under the top-level `steps` key
#' as a list member), the syntax closely follows the signature of the validation
#' function. Here is an example of how a complex call of `col_schema_match()` as
#' a validation step is expressed in R code and in the corresponding YAML
#' representation.
#'
#' R statement:
#'
#' ```r
#' agent %>%
#'   col_schema_match(
#'     schema = col_schema(
#'       a = "integer",
#'       b = "character"
#'     ),
#'     complete = FALSE,
#'     in_order = FALSE,
#'     is_exact = FALSE,
#'     actions = action_levels(stop_at = 1),
#'     label = "The `col_schema_match()` step.",
#'     active = FALSE
#'   )
#' ```
#'
#' YAML representation:
#'
#' ```yaml
#' steps:
#' - col_schema_match:
#'     schema:
#'       a: integer
#'       b: character
#'     complete: false
#'     in_order: false
#'     is_exact: false
#'     actions:
#'       stop_count: 1.0
#'     label: The `col_schema_match()` step.
#'     active: false
#' ```
#'
#' In practice, both of these will often be shorter as only the `schema`
#' argument requires a value. Arguments with default values won't be written to
#' YAML when using [yaml_write()] (though it is acceptable to include them with
#' their default when generating the YAML by other means). It is also possible
#' to preview the transformation of an agent to YAML without any writing to disk
#' by using the [yaml_agent_string()] function.
#'
#' @section Examples:
#'
#' For all examples here, we'll use a simple table with two columns: one
#' `integer` (`a`) and the other `character` (`b`). The following examples will
#' validate that the table columns abides match a schema object as created by
#' [col_schema()].
#'
#' ```{r}
#' tbl <-
#'   dplyr::tibble(
#'     a = 1:5,
#'     b = letters[1:5]
#'   )
#'
#' tbl
#' ```
#'
#' Create a column schema object with the helper function `col_schema()` that
#' describes the columns and their types (in the expected order).
#'
#' ```{r}
#' schema_obj <-
#'   col_schema(
#'     a = "integer",
#'     b = "character"
#'   )
#'
#' schema_obj
#' ```
#'
#' ## A: Using an `agent` with validation functions and then `interrogate()`
#'
#' Validate that the schema object `schema_obj` exactly defines the column names
#' and column types. We'll determine if this validation has a failing test unit
#' (there is a single test unit governed by whether there is a match).
#'
#' ```r
#' agent <-
#'   create_agent(tbl = tbl) %>%
#'   col_schema_match(schema = schema_obj) %>%
#'   interrogate()
#' ```
#'
#' Printing the `agent` in the console shows the validation report in the
#' Viewer. Here is an excerpt of validation report, showing the single entry
#' that corresponds to the validation step demonstrated here.
#'
#' \if{html}{
#' \out{
#' `r pb_get_image_tag(file = "man_col_schema_match_1.png")`
#' }
#' }
#'
#' ## B: Using the validation function directly on the data (no `agent`)
#'
#' This way of using validation functions acts as a data filter. Data is passed
#' through but should `stop()` if there is a single test unit failing. The
#' behavior of side effects can be customized with the `actions` option.
#'
#' ```{r}
#' tbl %>% col_schema_match(schema = schema_obj)
#' ```
#'
#' ## C: Using the expectation function
#'
#' With the `expect_*()` form, we would typically perform one validation at a
#' time. This is primarily used in **testthat** tests.
#'
#' ```r
#' expect_col_schema_match(tbl, scheam = schema_obj)
#' ```
#'
#' ## D: Using the test function
#'
#' With the `test_*()` form, we should get a single logical value returned to
#' us.
#'
#' ```{r}
#' tbl %>% test_col_schema_match(schema = schema_obj)
#' ```
#'
#' @family validation functions
#' @section Function ID:
#' 2-30
#'
#' @name col_schema_match
NULL

#' @rdname col_schema_match
#' @import rlang
#' @export
col_schema_match <- function(
    x,
    schema,
    complete = TRUE,
    in_order = TRUE,
    is_exact = TRUE,
    actions = NULL,
    step_id = NULL,
    label = NULL,
    brief = NULL,
    active = TRUE
) {

  if (!inherits(schema, "col_schema")) {

    stop(
      "A `col_schema` object must be provided to `schema`:\n",
      "* A schema can be defined using the `col_schema()` function",
      call. = FALSE
    )
  }

  # Incorporate `complete` and `in_order` options into
  # the `schema` object
  if (is.null(schema$`__complete__`) &&
      is.null(schema$`__in_order__`) &&
      is.null(schema$`__is_exact__`)) {

    schema <-
      structure(
        c(schema,
          list(
            `__complete__` = complete,
            `__in_order__` = in_order,
            `__is_exact__` = is_exact
          )
        ),
        class = c("match_options", class(schema))
      )
  }

  if (is_a_table_object(x)) {

    secret_agent <-
      create_agent(x, label = "::QUIET::") %>%
      col_schema_match(
        schema = schema,
        complete = complete,
        in_order = in_order,
        is_exact = is_exact,
        label = label,
        brief = brief,
        actions = prime_actions(actions),
        active = active
      ) %>%
      interrogate()

    return(x)
  }

  agent <- x

  brief <- resolve_brief(
    brief = brief, agent = agent,
    assertion_type = "col_schema_match"
  )

  # Normalize any provided `step_id` value(s)
  step_id <- normalize_step_id(step_id, columns = "column", agent)

  # Get the next step number for the `validation_set` tibble
  i_o <- get_next_validation_set_row(agent)

  # Check `step_id` value(s) against all other `step_id`
  # values in earlier validation steps
  check_step_id_duplicates(step_id, agent)

  # Add the validation step
  agent <-
    create_validation_step(
      agent = agent,
      assertion_type = "col_schema_match",
      i_o = i_o,
      columns_expr = NA_character_,
      column = NA_character_,
      values = schema,
      preconditions = NULL,
      actions = covert_actions(actions, agent),
      step_id = step_id,
      label = label,
      brief = brief,
      active = active
    )
}

#' @rdname col_schema_match
#' @import rlang
#' @export
expect_col_schema_match <- function(
    object,
    schema,
    complete = TRUE,
    in_order = TRUE,
    is_exact = TRUE,
    threshold = 1
) {

  fn_name <- "expect_col_schema_match"

  vs <-
    create_agent(tbl = object, label = "::QUIET::") %>%
    col_schema_match(
      schema = {{ schema }},
      complete = complete,
      in_order = in_order,
      is_exact = is_exact,
      actions = action_levels(notify_at = threshold)
    ) %>%
    interrogate() %>%
    .$validation_set

  x <- vs$notify %>% all()

  threshold_type <- get_threshold_type(threshold = threshold)

  if (threshold_type == "proportional") {
    failed_amount <- vs$f_failed
  } else {
    failed_amount <- vs$n_failed
  }

  if (inherits(vs$capture_stack[[1]]$warning, "simpleWarning")) {
    warning(conditionMessage(vs$capture_stack[[1]]$warning))
  }
  if (inherits(vs$capture_stack[[1]]$error, "simpleError")) {
    stop(conditionMessage(vs$capture_stack[[1]]$error))
  }

  act <- testthat::quasi_label(enquo(x), arg = "object")

  testthat::expect(
    ok = identical(!as.vector(act$val), TRUE),
    failure_message = glue::glue(
      failure_message_gluestring(
        fn_name = fn_name, lang = "en"
      )
    )
  )

  act$val <- object

  invisible(act$val)
}

#' @rdname col_schema_match
#' @import rlang
#' @export
test_col_schema_match <- function(
    object,
    schema,
    complete = TRUE,
    in_order = TRUE,
    is_exact = TRUE,
    threshold = 1
) {

  vs <-
    create_agent(tbl = object, label = "::QUIET::") %>%
    col_schema_match(
      schema = {{ schema }},
      complete = complete,
      in_order = in_order,
      is_exact = is_exact,
      actions = action_levels(notify_at = threshold)
    ) %>%
    interrogate() %>%
    .$validation_set

  if (inherits(vs$capture_stack[[1]]$warning, "simpleWarning")) {
    warning(conditionMessage(vs$capture_stack[[1]]$warning))
  }
  if (inherits(vs$capture_stack[[1]]$error, "simpleError")) {
    stop(conditionMessage(vs$capture_stack[[1]]$error))
  }

  all(!vs$notify)
}

#' Generate a table column schema manually or with a reference table
#'
#' @description
#'
#' A table column schema object, as can be created by `col_schema()`, is
#' necessary when using the [col_schema_match()] validation function (which
#' checks whether the table object under study matches a known column schema).
#' The `col_schema` object can be made by carefully supplying the column names
#' and their types as a set of named arguments, or, we could provide a table
#' object, which could be of the `data.frame`, `tbl_df`, `tbl_dbi`, or
#' `tbl_spark` varieties. There's an additional option, which is just for
#' validating the schema of a `tbl_dbi` or `tbl_spark` object: we can validate
#' the schema based on R column types (e.g., `"numeric"`, `"character"`, etc.),
#' SQL column types (e.g., `"double"`, `"varchar"`, etc.), or Spark SQL column
#' types (`"DoubleType"`, `"StringType"`, etc.). This is great if we want to
#' validate table column schemas both on the server side and when tabular data
#' is collected and loaded into R.
#'
#' @param ... *Column-by-column schema definition*
#'
#'   `<multiple expressions>` // **required** (or, use `.tbl`)
#'
#'   A set of named arguments where the names refer to column names and
#'   the values are one or more column types.
#'
#' @param .tbl *A data table for defining a schema*
#'
#'   `obj:<tbl_*>` // **optional**
#'
#'   An option to use a table object to define the schema. If this is provided
#'   then any values provided to `...` will be ignored. This can either be a
#'   table object, a table-prep formula.This can be a table object such as a
#'   data frame, a tibble, a `tbl_dbi` object, or a `tbl_spark` object.
#'   Alternatively, a table-prep formula (`~ <tbl reading code>`) or a
#'   function (`function() <tbl reading code>`) can be used to lazily read in
#'   the table at interrogation time.
#'
#' @param .db_col_types *Use R column types or database column types?*
#'
#'   `singl-kw:[r|sql]` // *default:* `"r"`
#'
#'   Determines whether the column types refer to R column types (`"r"`) or SQL
#'   column types (`"sql"`).
#'
#' @section Examples:
#'
#' Create a simple table with two columns: one `integer` and the other
#' `character`.
#'
#' ```{r}
#' tbl <-
#'   dplyr::tibble(
#'     a = 1:5,
#'     b = letters[1:5]
#'   )
#'
#' tbl
#' ```
#'
#' Create a column schema object that describes the columns and their types (in
#' the expected order).
#'
#' ```{r}
#' schema_obj <-
#'   col_schema(
#'     a = "integer",
#'     b = "character"
#'   )
#'
#' schema_obj
#' ```
#'
#' Validate that the schema object `schema_obj` exactly defines the column names
#' and column types of the `tbl` table.
#'
#' ```r
#' agent <-
#'   create_agent(tbl = tbl) %>%
#'   col_schema_match(schema_obj) %>%
#'   interrogate()
#' ```
#'
#' Determine if this validation step passed by using `all_passed()`.
#'
#' ```r
#' all_passed(agent)
#' ```
#'
#' ```
#' ## [1] TRUE
#' ```
#'
#' We can alternatively create a column schema object from a `tbl_df` object.
#'
#' ```r
#' schema_obj <-
#'   col_schema(
#'     .tbl = dplyr::tibble(
#'       a = integer(0),
#'       b = character(0)
#'     )
#'   )
#' ```
#'
#' This should provide the same interrogation results as in the previous
#' example.
#'
#' ```r
#' create_agent(tbl = tbl) %>%
#'   col_schema_match(schema_obj) %>%
#'   interrogate() %>%
#'   all_passed()
#' ```
#'
#' ```
#' ## [1] TRUE
#' ```
#'
#' @family Utility and Helper Functions
#' @section Function ID:
#' 13-1
#'
#' @export
col_schema <- function(
    ...,
    .tbl = NULL,
    .db_col_types = c("r", "sql")
) {

  db_col_types <- match.arg(.db_col_types)

  x <- rlang::list2(...)

  # Transform SQL column types to lowercase to allow
  # both uppercase and lowercase conventions while
  # standardizing the input
  if (db_col_types == "sql") {
    x <- lapply(x, tolower)
  }

  # Apply the `col_schema` and the `r_type`/`sql_type` classes
  class(x) <- c(paste0(db_col_types, "_type"), "col_schema")

  if (!is.null(.tbl)) {

    # Validate .tbl object but first materialize the table
    .tbl <- materialize_table(tbl = .tbl)

    # Generate schema from tbl object
    if (inherits(.tbl, "data.frame")) {

      x <- create_col_schema_from_df(tbl = .tbl)

      # Apply the `col_schema` class
      class(x) <- c("r_type", "col_schema")
    }

    if (inherits(.tbl, "tbl_dbi") ||
        inherits(.tbl, "tbl_spark") ||
        inherits(.tbl, "ArrowObject")) {

      tbl_info <- get_tbl_information(tbl = .tbl)

      x <-
        switch(
          db_col_types,
          "r" = create_col_schema_from_df(tbl = .tbl),
          "sql" = col_schema_from_names_types(
            names = tbl_info$col_names,
            types = tbl_info$db_col_types
          )
        )

      # Apply the `col_schema` and the `r_type`/`sql_type` classes
      class(x) <- c(paste0(db_col_types, "_type"), "col_schema")
    }
  }

  x
}

r_col_type <- function(type) {
  # Generate a standardized vector for an `r_type`
}

db_col_type <- function(db_type) {
  # Generate a standardized vector for an `db_col_type`
}

# Generates a list of R column types from any type of table
create_col_schema_from_df <- function(tbl) {

  if (is_a_table_object(tbl) && !is_tbl_df(tbl)) {

    tbl <-
      tbl %>%
      utils::head(1) %>%
      dplyr::collect()
  }

  lapply(tbl, class)
}

col_schema_from_names_types <- function(names, types) {
  as.list(stats::setNames(types, names))
}
